KR100849827B1 - Subminiature optical system - Google Patents

Abstract

A subminiature optical system is provided to reduce the weight, facilitate the manufacture, and enable mass production by using a plurality of plastic lenses. A subminiature optical system includes first to fourth lenses(L1~L4) sequentially arranged from an object side. The first lens has positive refractive power. The second lens has negative refractive power and an upper surface thereof is upward concave. The third lens has negative refractive power. The fourth lens has positive refractive power. The second and third lenses are made of flint based material. At least one of the first and fourth lenses has an aspheric surface. The first, third, and fourth lenses are plastic lenses. The second lens is a glass lens.

Description

Subminiature imaging optical system {SUBMINIATURE OPTICAL SYSTEM}

1 is a lens configuration diagram of a microscopic imaging optical system according to a first embodiment of the present invention.

FIG. 2 illustrates a first aberration diagram of the first embodiment shown in FIG.

   (a) is spherical aberration, (b) is astigmatism, and (c) is distortion.

3 is an MTF graph of the first embodiment shown in FIG.

4 is a lateral chromatic aberration diagram of the first embodiment shown in FIG.

5 is a lens configuration diagram of a microscopic imaging optical system according to a second embodiment of the present invention.

FIG. 6 is a view illustrating a second aberration diagram of the second embodiment illustrated in FIG. 5.

   (a) is spherical aberration, (b) is astigmatism, and (c) is distortion.

7 is an MTF graph of the second embodiment shown in FIG.

FIG. 8 is a side chromatic aberration diagram of the second embodiment shown in FIG. 5; FIG.

Explanation of symbols on the main parts of the drawings

L1 ... first lens L2 ... second lens

L3 ... third lens L4 ... fourth lens

S ... opening aperture OF ... optical filter

IP ... Top

1,2,3,4,5,6,7,8,9,10,11,12 ... face number

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system, and more particularly, to a microscopic imaging optical system mounted on a mobile communication terminal, a PDA, or the like and used for a surveillance camera, a digital camera, or the like.

Recently, a camera module for a communication terminal, a digital still camera (DSC, digital still camera), a camcorder, and a PC camera (image pickup device included in a personal computer) have been studied in relation to an image pickup system. The most important component for such an image pickup system to obtain an image is a lens system that forms an image.

Such a lens system requires a high performance in terms of resolution, image quality, etc., but the configuration of the lens is complicated. However, when the lens system is structurally or optically complicated, there is a problem in that the size is increased and the size thereof is opposed to miniaturization and thinning.

For example, miniaturization of the entire module is essential for the camera module mounted in the mobile phone to increase its mountability. In addition, the image sensor of the CCD or CMOS is increasingly being reduced in size and the pixel size is reduced, and the corresponding lens system must not only require miniaturization and thinning, but also high resolution and excellent optical performance.

In this case, when using a 3 million pixel imaging device (CCD or CMOS), optical performance and miniaturization can be satisfied with a lens configuration of 3 sheets or less, but 3 or less sheets are required for a high resolution imaging device (CCD or CMOS) having 5 million pixels or more. When the lens of is used, the refractive power of each lens should be large, and accordingly difficult to process the lens, there is a problem that it is difficult to satisfy high performance and miniaturization at the same time. In addition, despite the configuration of four or more lenses, when using a spherical lens, there is a problem that the total length of the optical system is increased, making it difficult to achieve miniaturization.

Accordingly, there is a need for a lens system for a miniature camera module that can simultaneously realize miniaturization and optical performance.

The present invention is to solve the above problems, it is an object to provide a lens system for a compact camera module that can implement high resolution and miniaturization with only four lenses, excellent optical performance.

In addition, an object of the present invention is to provide a lens system for a small size and light weight ultra compact camera module by using at least three or more plastic lenses, low production cost and mass production.

As one aspect for achieving the above object, the present invention,

It is arranged in order from an object side to an upper surface front,

A first lens having positive refractive power;

A second lens having negative refractive power and having an image side concave toward the image side;

A third lens having negative refractive power; And

Fourth lens having positive refractive power

Includes, wherein the second lens and the third lens provides the ultra-small imaging optical system, characterized in that to satisfy the following Conditional Expression 1 and Conditional Expression 2, respectively.

[Condition 1] 20 <V2 <50

[Condition 2] 20 <V3 <30

(V2: Abbe number of the second lens, V3: Abbe number of the third lens)

Preferably, at least one surface of each of the first lens, the third lens, and the fourth lens may be formed as an aspherical surface.

Also, preferably, the first lens, the third lens, and the fourth lens are plastic lenses, the second lens may be composed of glass lenses, and the first to fourth lenses may be all composed of plastic lenses. have.

Preferably, the aperture stop may be provided in front of the object side of the first lens.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a lens configuration diagram showing a first embodiment of a microscopic imaging optical system according to the present invention. In the following lens configuration, the thickness, size, and shape of the lens have been somewhat exaggerated for explanation, and in particular, the shape of the spherical or aspherical surface shown in the lens configuration is merely an example and is not limited thereto.

In general, the camera module has at least one lens, a predetermined space formed therein, a housing accommodating the lens, an image sensor corresponding to an imaging surface by the lens, and a fixed installation at the other end of the housing, wherein the image is fixed on one surface of the camera module. The sensor may be mounted to a circuit board for processing an image sensed by the image sensor.

The present invention relates to an ultra-small imaging optical system used in such a miniature camera module.

As shown in FIG. 1, the ultra-small imaging optical system according to the present invention has a positive refractive power (L1), a second lens (L2) having a negative refractive power and an image side concave to the image side, and a negative refractive power. A third lens L3 and a fourth lens L4 having positive refractive power are included, and an aperture stop S is provided in front of the object side of the first lens L1. At least one surface of each of the first, third, and fourth lenses L1, L3, and L4 is preferably formed as an aspherical surface.

Here, at least three lenses of the first to fourth lenses L1 to L4 may be configured as plastic lenses, and the first, third and fourth lenses L1 to L4 having aspherical surfaces may be plastic lenses. It is preferable to configure the second lens L2 to a glass lens. In addition, all of the first to fourth lenses L1 to L4 may be formed of plastic lenses. This has the advantage of reducing manufacturing costs, enabling mass production, and implementing small, lightweight optical systems. In particular, by using an aspherical lens, it is possible to improve the resolution of the lens and at the same time reduce distortion and spherical aberration, and to realize a compact and excellent optical system.

Meanwhile, an optical filter OF corresponding to an infrared filter, a cover glass, or the like is provided between the fourth lens L4 and the image surface IP.

In addition, the upper surface IP corresponds to an image sensor such as a CCD and a CMOS.

In addition, since the area of the lens surface most exposed to the object side is small by arranging the position of the aperture stop in front of the object side of the first lens L1, it is easy to manage the infiltration of foreign objects and the like. By being located close to the top surface, it is possible to miniaturize the window of the external mechanism for fixing the camera module. In addition, the higher the resolution, the smaller the pixel size of the image sensor is required to have a brighter optical system (lens with a small F number), the aperture is located in front of the object side is an advantage that is easy to manufacture a bright optical system have.

Under this overall configuration, the effects of the following Conditional Expressions 1 and 2 will be described.

[Condition 1]

20 <V2 <50

[Condition Formula 2]

20 <V3 <30

In the above Conditional Expressions 2 and 3, V2 represents the Abbe number of the second lens L2, and V3 represents the Abbe number of the third lens L3.

Conditional Expressions 2 and 3 define conditions relating to the Abbe number of the second lens L2 and the third lens L3.

Optical materials can be largely divided into two types, and can be divided into crown series having Abbe number of 50 or more and Flint series having Abbe number of less than 50. Of these, Flint-based optical materials have a large color dispersion with Abbe number of less than 50. According to the present invention, lateral chromatic aberration can be improved by using a flint-based medium having a large color dispersion so as to have negative refractive power in the second and third lenses L2 and L3 located at the second and third positions from the object side. . In addition, among the currently known optical materials, there is no optical material having an Abbe number of 20 or less.

Hereinafter, the present invention will be described with reference to specific numerical examples.

As described above, Embodiments 1 and 2, as described above, have a positive refractive power (L1), a second lens (L2) having a negative refractive power and an image side concave upward, and a third having a negative refractive power. A lens L3 and a fourth lens L4 having positive refractive power are included, and an aperture stop S is provided in front of the object side of the first lens L1. In addition, an optical filter OF corresponding to an infrared filter, a cover glass, or the like is provided between the fourth lens L4 and the image surface IP, and the image surface IP corresponds to an image sensor such as a CCD or a CMOS. .

The aspherical surface used in each of the following examples is obtained from well-known Equation 1, and is used in the Conic constant (K) and the aspherical surface coefficients (A, B, C, D, E, F) and The number following is the power of ten. For example, E + 01 represents 10 ¹ and E-02 represents 10 ⁻² .

Z: Distance from the vertex of the lens to the optical axis direction

Y: distance in the direction perpendicular to the optical axis

c: inverse of the radius of curvature r at the vertex of the lens

K: Conic constant

A, B, C, D, E, F: Aspheric coefficient

In addition, in the MTF graph of each embodiment below, the MTF (Modulation Transfer Function) depends on the spatial frequency of cycles per millimeter, and the value defined by the following equation (2) between the maximum intensity (Max) and the minimum intensity (Min) of light. to be.

In other words, if the MTF is 1, it is most ideal. If the MTF value decreases, the resolution drops.

First Embodiment

Table 1 below shows a numerical example of the optical system according to the first embodiment of the present invention. 1 is a lens configuration diagram of a microscopic imaging optical system according to a first embodiment of the present invention, and FIGS. 2A to 2C show aberration diagrams of the optical systems shown in Table 1 and FIG. 3 is an MTF graph of the optical system shown in Table 1 and FIG. 4 is a lateral chromatic aberration diagram of the optical system shown in Table 1 and FIG.

In the first embodiment, the F number FNo is 2.85, the angle of view is 60 degrees, and the distance TL from the object-side surface 2 to the image surface 12 of the first lens L1 is 5.95. Mm and the effective focal length f of the optical system are 4.8 mm. In addition, the first lens L1, the third lens L3, and the fourth lens L4 are made of a plastic material, and the second lens L2 is made of a glass material.

In Table 1, * denotes an aspherical surface, and in the first embodiment, the object side and image refraction surfaces 2 and 3 of the first lens L1, the object side and image refraction surfaces 6 and 7 of the third lens L3, The object side and the image-side refractive surfaces 8 and 9 of the fourth lens L4 are aspherical surfaces.

The aspherical coefficients of the first embodiment according to Equation 1 are shown in Table 2 below.

Example 2

Table 3 below shows numerical examples of the optical system according to the second embodiment of the present invention. 5 is a lens configuration diagram of the ultra-small imaging optical system according to the second embodiment of the present invention, and FIGS. 6A to 6C show aberration diagrams of the optical systems shown in Tables 3 and 4. 7 is an MTF graph of the optical system shown in Table 3 and FIG. 5. 8 is a lateral chromatic aberration diagram of the optical system shown in Table 3 and FIG.

In the second embodiment, the F number FNo is 2.8, the angle of view is 61.5 degrees, and the distance TL from the object-side surface 2 to the image surface 12 of the first lens L1 is 5.83. Mm and the effective focal length f of the optical system are 4.81 mm. In addition, in the second embodiment, all of the first to fourth lenses L1 to L4 are made of a plastic material.

In Table 3, * denotes an aspherical surface, and in the second embodiment, the object side and image refraction surfaces 2 and 3 of the first lens L1, the object side and image refraction surfaces 6 and 7 of the third lens L3, The object side and the image-side refractive surfaces 8 and 9 of the fourth lens L4 are aspherical surfaces.

The aspherical coefficients of the second embodiment according to Equation 1 are shown in Table 4 below.

As shown in FIG. 2 and FIG. 6, the optical system having excellent characteristics of the first aberration can be obtained through the above embodiments.

On the other hand, the values of the conditional formulas 1 to 5 for the first to the second embodiment is shown in Table 5 below.

First embodiment Second embodiment Conditional Expression 1 27.38 23.42 Conditional Expression 2 27.3 27.3

As shown in Table 5, it can be seen that the first and second embodiments of the present invention satisfy conditional expressions 1 to 5.

As described above, according to the present invention, it is suitable for a micro optical device such as a camera for a mobile phone using an image sensor such as CCD or CMOS, and minimizes various aberrations by adjusting the radius of curvature of each refractive surface of the lens constituting the optical system and using an aspherical surface. In addition, there is an effect that high resolution, high definition images can be obtained.

In addition, by using a large number of plastic lenses, not only the weight can be reduced, but also the production is easy, mass production is possible, and the manufacturing cost is low.

While the invention has been shown and described with respect to particular embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I want to make it clear.

Claims (5)

It is arranged in order from an object side to an upper surface front, A first lens having positive refractive power; A second lens having negative refractive power and having an image side concave toward the image side; A third lens having negative refractive power; And Fourth lens having positive refractive power Wherein the second lens and the third lens are made of a flint-based material, and satisfy the following Conditional Expressions 1 and 2, respectively, wherein an aperture stop is provided in front of the object side of the first lens. Ultra-small imaging optics. [Condition 1] 20 <V2 <50 [Condition 2] 20 <V3 <30 (V2: Abbe number of the second lens, V3: Abbe number of the third lens) The method of claim 1, At least one surface of each of the first lens, the third lens, and the fourth lens is an aspherical surface, wherein the ultra-compact optical system. The method according to claim 1 or 2, And the first lens, the third lens, and the fourth lens are plastic lenses, and the second lens is a glass lens. The method according to claim 1 or 2, The first to fourth lenses are ultra-small imaging optical system, characterized in that the plastic lens. delete

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